It is known that more than one power supply can be used to provide power to a common power bus. Care must be taken to avoid having one circuit attempt to provide all the power. Such a condition could cause that circuit to fail. For example, FIG. 1 shows circuit for a Unitrode UC1907, UC2907 and UC3907 integrated circuit. The Unitrode approach allows multiple power supply modules to be coupled together in parallel. Each of the parallel power supply module only supplies a proportionate share of the total load current. A current from each power supply module is sensed. The controller determines which of the power supply modules would normally have the highest current value and designates it as the master. The power supply module with the highest current is the one that is most likely to fail first. Upon determination of the master module, the other modules are adjusted have provide current within 2.5% of the current value of the master.
This Unitrode approach requires a sixteen pin package to provide sufficient inputs and outputs to control the power supply modules. It is well known that the cost of an integrated circuit is proportional in some measure to the number of these so-called I/O pins. As such it is desirable to reduce the number of pins.